The UV absorbers of the 2H-benzotriazole and benzophenone type have long been known as very effective light stabilizers for a host of organic materials and have enjoyed considerable commercial success.
The description, preparation and uses of the 2H-benzotriazoles UV absorbers are taught in U.S. Pat. Nos. 3,004,896; 3,055,896; 3,072,585; 3,074,910; 3,189,615; 3,230,194; 4,127,586; 4,226,763; 4,278,589; 4,315,848; 4,383,863; 4,675,352; 4,681,905 and 4,853,471.
The description, preparation and uses of the benzophenone UV absorbers are found in a comprehensive review by G. R. Lapin in the "Encyclopedia of Polymer Science and Technology", N. Bikales, editor, John Wiley-Interscience, New York, Vol. 14, 1971, pp 125-148.
In some circumstances, the benzotriazole and benzophenone UV absorbers exhibit limited compatibility with certain substrates, and/or an excessive tendency to exude, sublime or volatilize away during processing of stabilized compositions into sheets, films, fibers or other pellicles when processing must be done at elevated temperatures. Likewise, such compounds may also suffer undue loss by volatilization or sublimation from fabricated structures, particularly thin films, coatings or fibers, especially when such structures are subjected to elevated temperatures during use.
Attempts have been made to increase compatibility and to reduce volatilization by modifying the structure of the benzotriazole. U.S. Pat. No. 3,230,194 teaches that substitution of a higher alkyl group (tert-octyl) for a lower alkyl group (methyl) improves compatibility and performance of the substituted benzotriazole in polyethylene.
Likewise in U.S. Pat. Nos. 4,278,590; 4,283,327 and 4,383,863, 2-(2-hydroxy-3,5-di-tert-octylphenyl)-2H-benzotriazole is shown to exhibit an excellent combination of compatibility with and/or solubility in numerous polymer substrates along with superior resistance to loss from stabilization during high temperature processing, in end-use applications where coating or films of the stabilized compositions are exposed to ambient weathering and light, and in photographic applications.
U.S. Pat. No. 4,675,352 teaches that liquid benzotriazoles of low volatility are prepared by the alkylation of preformed 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole.
U.S. Pat. Nos. 3,936,305; 4,681,905; 4,684,680; 4,684,679 and 5,108,835 teach the 2,2'-methylene-bis-[4-hydrocarbyl-6-(benzotriazol-2-yl)phenols] having high molar activities and low volatility.
U.S. Pate. Nos. 3,399,237 and 4,169,089 and Japanese patent applications Sho 53-113849; 57-6470; 49-78692; 50-74579 and 50-86487 teach the corresponding class of low volatility compounds with high molar activities which are the methylene-bis(2-hydroxybenzophenones).
U.S. Pat. No. 5,166,355 describes a process for making 2,2'-methylene-bis-[6-(2H-benzotriazo-2-yl)-4hydrocarbylphenol] or 5,5'-methylene-bis-(2-hydroxy-4-alkoxybenzophenone using bis(dialkylamino)methane.
The instant compounds exhibit low volatility and excellent absorption characteristics in a broad ultraviolet range. Their photographic inertness is particularly useful in photographic compositions, expecially in protecting color dye images against the harmful effects of ultraviolet light.